Replacement of the cathode ray tube with a flat panel screen requires a display technology which simultaneously makes it possible to achieve a high resolution, i.e. more than 1 000 lines, a high brightness ( greater than 200 Cd/m2), a high contrast ( greater than 100:1), a high frame rate ( greater than 60 Hz), an adequate color representation ( greater than 16 million), a large image format ( greater than 40 cm), a low power consumption and a wide viewing angle, at low production costs. At present, there is no technology which fully satisfies all these features simultaneously.
Many manufacturers have developed screens which are based on nematic liquid crystals and have been used in recent years in the field of notebook PCs, personal digital assistants, desktop monitors etc. Use is made here of the technologies STN (supertwisted nematics), AM-TN (active matrixxe2x80x94twisted nematics), AM-IPS (active matrixxe2x80x94in-plane switching) and AM-MVA (active matrixxe2x80x94multidomain vertically aligned), which are described in detail in the relevant literature (see, for example, T. Tsukuda, TFT/LCD: Liquid Crystal Displays Addressed by Thin-Film Transistors, Gordon and Breach 1996, ISBN 2-919875-01-9 and the references cited therein; SID Symposium 1997, ISSN-0097-966X and the references cited therein). Furthermore, mention should be made of the technologies PDP (plasma display panel), PALC (plasma addressed liquid crystal), ELD (electro-luminescent display), FED (field emission display) etc., which are also explained in the above-cited SID report.
Clark and Lagerwall (U.S. Pat. No. 4,376,924) were able to show that the use of ferroelectric liquid crystals (FLC) in very thin cells results in opto-electrical switching or display elements which have response times which are faster by a factor of up to 1 000 compared with conventional TN (twisted nematic) cells (see, for example, EP-A 0 032 362). Owing to this and other favorable properties, for example the possibility of bistable switching and the fact that the contrast is virtually independent of the viewing angle, FLCs are basically suitable for areas of application such as computer displays and TV sets, as shown by a monitor marketed in Japan by Canon since May 1995.
The use of FLCs in electro-optical or fully optical components requires either compounds which form tilted or orthogonal smectic phases and are themselves optically active, or the induction of ferroelectric smectic phases by doping compounds which, although forming such smectic phases, are not themselves optically active, with optically active compounds. The desired phase should be stable over the broadest possible temperature range to ensure that the display has a broad operating range.
The individual pixels of an LC display are usually arranged in an x,y matrix formed by the arrangement of a series of electrodes (conductor tracks) along the rows and a series of electrodes along the columns on the upper or lower side of the display. The points of interception of the horizontal (row) electrodes and the vertical (column) electrodes form, addressable pixels.
This pixel arrangement is usually referred to as a passive matrix. For addressing, various multiplex schemes have been developed, as described, for example, in Displays 1993, vol. 14, No. 2, pp. 86-93, and Kontakte 1993 (2), pp. 3-14. Passive matrix addressing has the advantage of simpler display production and consequently lower production costs, but the disadvantage that passive addressing can only be carried out line by line, which results in the addressing time for the entire screen with N lines being N times the line addressing time. For usual line addressing times of about 50 microseconds, this means a screen addressing time of about 60 milliseconds in, for example, the HDTV (high definition TV, 1152 lines) standard, i.e. a maximum frame rate of about 16 Hz, too slow for displaying moving images. In addition, display of gray shades is often difficult. At the FLC conference in Brest, France (Jul. 20-24, 1997, see Abstract Book 6th International Conference on Ferroelectric Liquid Crystals, Brest/France), a passive FLC display with digital gray shades was shown by Mizutani et al., in which each of the RGB pixels (RGB=red, green, blue) was divided into sub-pixels, allowing the display of gray shades in digital form through partial switching. Using three basic colors (red, green, blue), N gray shades result in 3N colors. The disadvantage of this method is the considerable increase in the number of screen drivers necessary and thus in the costs (in the case of the display shown in Brest, three times as many drivers were necessary as in a standard FLC display without digital gray shades).
In so-called active-matrix technology (AMLCD), a nonstructured substrate is usually combined with an active-matrix substrate. An electrically non-linear element, for example a thin-film transistor, is integrated into each pixel of the active-matrix substrate. The non-linear elements can also be diodes, metal-insulator-metal and similar elements, which are advantageously produced by thin-film processes and are described in the relevant literature (see, for example, T. Tsukuda, TFT/LCD: Liquid Crystal Displays Addressed by Thin-Film Transistors, Gordon and Breach 1996, ISBN 2-919875-01-9, and the references cited therein).
Active-matrix LCDs are usually operated with nematic liquid crystals in TN (twisted nematics), ECB (electrically controlled birefringence), VA (vertically aligned) or IPS (in-plane switching) mode. In each case, the active matrix generates an electric field of individual strength on each pixel, producing a change in alignment and thus a change in birefringence, which is in turn visible in polarized light. A severe disadvantage of these processes is the poor video capability, i.e. the excessively slow response times of nematic liquid crystals.
For this and other reasons, liquid-crystal displays based on a combination of ferroelectric liquid-crystal materials and active-matrix elements have been proposed, for example in WO 97/12355 or Ferroelectric 1996, 179, 141-152, W. J. A. M. Hartmann (IEEE Trans. Electron. Devices 1989, 36 (9; Pt. 1), 1895-9, and Dissertation, Eindhoven, The Netherlands, 1990).
Hartmann used a combination of the so-called xe2x80x9cquasi-bookshelf geometryxe2x80x9d (QBG) of an FLC and a TFT (thin-film transistor) active matrix to simultaneously achieve high response speed, gray shades and high transmission. However, the QBG is not stable over a broad temperature range, since the temperature dependence of the smectic layer thickness disrupts or rotates the field-induced layer structure. Moreover, Hartmann utilizes an FLC material having a spontaneous polarization of more than 20 nC/cm2, which, for pixels having realistic dimensions of, for example, 0.01 mm2, leads to high electrical charges (at saturation, Q=2 AP, A=pixel area, P=spontaneous polarization). With low-cost amorphous silicon TFTs, for example, these high charges cannot reach the pixel in the course of the opening time of the TFT. For these reasons, this technology has not been pursued any further to date.
While Hartmann utilizes the charge-controlled bistability to display a virtually continuous gray scale, Nito et al. have suggested a monostable FLC geometry (Journal of the SID, 1/2, 1993, pp. 163-169) in which the FLC material is aligned by means of relatively high voltages such that only a single stable position results from which a number of intermediate states are generated by application of an electric field via a thin-film transistor. These intermediate states correspond to a number of different brightness values (gray shades) when the cell geometry is matched between crossed polarizers.
The disadvantage of the paper by Nito et al. is the occurrence of a streaky texture which limits the contrast and brightness of this cell (see FIG. 8 of the abovementioned citation). While it is possible to correct the disadvantageous streaky texture by treatment with a high electric voltage (20-50 V) in the nematic or cholesteric phase (see page 168 of the abovementioned citation), such a field treatment is unsuitable for mass production of screens and usually does not result in temperature-stable textures either. Furthermore, this method produces switching only in an angle range of up to a maximum of once the tint angle, which is about 22xc2x0 in the case of the material used by Nito et al. (cf. p. 165, FIG. 6) and thus produces a maximum transmission of only 50% of the transmission of two parallel polarizers.
The object of the present invention is to provide a preferably chiral smectic active-matrix liquid-crystal display, containing a preferably chiral smectic liquid-crystal mixture, where the liquid-crystal mixture makes it possible to achieve a very high maximum transmission and a very high contrast and a constant threshold voltage over a broad temperature range.
In particular, a ferroelectric active-matrix liquid-crystal display containing a ferroelectric liquid-crystal mixture is to be provided where the liquid-crystal mixture assumes a monostable position, but without forming any streaky texture, is temperature-stable and makes it possible to achieve a very high maximum transmission and a very high contrast and a constant threshold voltage over a broad temperature range.
This object is achieved according to the invention by a chiral smectic active-matrix display containing a liquid-crystal layer having a tilt angle which is virtually constant over a broad temperature range and a virtually constant layer leaning angle, where the liquid-crystal layer comprises at least one compound of the formula (I) below.
Expressly included is the advantageous use of the novel materials and mixtures for active-matrix displays, antiferroelectric displays and twisted smectic displays.
In particular, the object is achieved by a chiral smectic active-matrix display containing a liquid-crystal layer in the form of a monostable monodomain having a tilt angle which is virtually constant over a broad temperature range, and a virtually constant layer leaning angle, where the liquid-crystal layer comprises at least one compound of the formula (I) below.
The active-matrix display contains a chiral smectic liquid-crystal mixture comprising at least one compound of the general formula (I)
R1xe2x80x94(A1xe2x80x94M1)axe2x80x94(A2xe2x80x94M2)bxe2x80x94A3xe2x80x94Xxe2x80x94B1xe2x80x94(B2)cxe2x80x94R2xe2x80x83xe2x80x83(I)
where the symbols are as defined below:
R1, R2 are, independently of one another, identical or different and are each
a) hydrogen, fluorine or CN
a straight-chain or branched alkenyl, alkenyloxy, alkyl or alkyloxy radical (with or without asymmetric carbon atoms) having 2 to 16 carbon atoms, where
b1) one or two nonterminal xe2x80x94CH2xe2x80x94 groups may be replaced by xe2x80x94Oxe2x80x94, xe2x80x94OC(xe2x95x90O)xe2x80x94, xe2x80x94(Cxe2x95x90O), xe2x80x94C(xe2x95x90O)Oxe2x80x94, xe2x80x94Si(CH3)2xe2x80x94, xe2x80x94CH(Cl)xe2x80x94 and/or one or two xe2x80x94CH2xe2x80x94 groups may be replaced by xe2x80x94CHxe2x95x90CHxe2x80x94 or xe2x80x94Cxe2x89xa1Cxe2x80x94
xe2x80x83and one or more H atoms may be replaced by F and/or
b2) one or more xe2x80x94CH2xe2x80x94 groups may be replaced by phenylene-1,4-diyl (unsubstituted, monosubstituted or disubstituted by F), phenylene-1,3-diyl (unsubstituted, monosubstituted or disubstituted by F), cyclohexane-1,4-diyl (unsubstituted or monosubstituted by F or CN) or cyclopropane-1,2-diyl
xe2x80x83and one or more H atoms may be replaced by F
xe2x80x83with the provisos that only one of the radicals R1, R2 can be hydrogen, F or CN and that two adjacent xe2x80x94CH2xe2x80x94 groups cannot be replaced by xe2x80x94Oxe2x80x94
M1, M2 are, independently of one another, identical or different and are each xe2x80x94C(xe2x95x90O)Oxe2x80x94, xe2x80x94OC(xe2x95x90O)xe2x80x94, xe2x80x94CH2Oxe2x80x94, xe2x80x94OCH2xe2x80x94, xe2x80x94CF2Oxe2x80x94, xe2x80x94OCF2xe2x80x94, xe2x80x94CH2CH2xe2x80x94, xe2x80x94CF2CF2xe2x80x94, xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94CHxe2x95x90CFxe2x80x94, xe2x80x94CFxe2x95x90CFxe2x80x94, xe2x80x94Cxe2x89xa1Cxe2x80x94, xe2x80x94CH2CH2C(xe2x95x90O)Oxe2x80x94, xe2x80x94OC(xe2x95x90O)CH2CH2xe2x80x94, xe2x80x94(CH2)4xe2x80x94, xe2x80x94OCH2CH2CH2xe2x80x94, xe2x80x94CH2CH2CH2Oxe2x80x94, xe2x80x94OCH2CF2CH2xe2x80x94, xe2x80x94CH2CF2CH2Oxe2x80x94 or a single bond
A1, A2, A3 are, independently of one another, identical or different and are each cyclohexane-1,4-diyl (unsubstituted or monosubstituted by F, CH3, CN), cyclohex-1-ene-1,4-diyl, cyclohex-2-ene-1,4-diyl, 2-oxocyclohexane-1,4-diyl, 2-cyclohexen-1-one-3,6-diyl, 1-alkyl-1-silacyclohexane-1,4-diyl, bicyclo[2.2.2]octane-1,4-diyl, spiro[4.5]-decane-2,8-diyl, spiro[5.5]undecane-3,9-diyl, phenylene-1,4-diyl (unsubstituted, monosubstituted or disubstituted by ON, CH3, CF3, OCH3, unsubstituted, monosubstituted, disubstituted, trisubstituted or tetrasubstituted by F), phenylene-1,3-diyl (unsubstituted, monosubstituted or disubstituted by CN, CH3, CF3, OCF3, unsubstituted, monosubstituted, disubstituted, trisubstituted or tetrasubstituted by F), thiophene-2,5-diyl, thiophene-2,4-diyl, (1,3,4)-oxadiazole-2,5-diyl, (1,3,4)-thiadiazole-2,5-diyl, 1,3-thiazole-2,5-diyl, 1,3-thiazole-2,4-diyl, (1,3)-oxazole-2,5-diyl, isoxazole-2,5-diyl, indane-2,6-diyl, naphthalene-2,6-diyl (unsubstituted, monosubstituted or disubstituted by F or CN), 1,2,3,4-tetrahydronaphthalene-2,6-diyl, decaline-2,6-diyl, pyrimidine-2,5-diyl (unsubstituted or monosubstituted by F), pyridine-2,5-diyl (unsubstituted, monosubstituted or disubstituted by F), pyrazine-2,5-diyl (unsubstituted or monosubstituted by F), pyridazine-3,6-diyl, quinoline-2,6-diyl, quinoline-3,7-diyl, isoquinoline-3,7-diyl, quinazoline-2,6-diyl, 5,6,7,8-tetrahydroquinazoline-2,6-diyl, quinoxaline-2,6-diyl, 1,3-dioxane-2,5-diyl (unsubstituted or monosubstituted by CN), benzothiazole-2,6-diyl, piperidine-2,4-diyl, piperazine-1,4-diyl
B1 is cyclohexane-1,4-diyl (unsubstituted, monosubstituted or disubstituted by F, CH3, CN), perfluorocyclohexane-1,4-diyl, cyclohex-1-ene-1,4-diyl, cyclohex-2-ene-1,4-diyl, 1-alkyl-1-silacyclohexane-1,4-diyl, bicyclo[2.2.2]octane-1,4-diyl, cyclopentane-1,3-diyl, cycloheptane-1,4-diyl, tetrahydrofuran-2,5-diyl, tetrahydrofuran-2,4-diyl, phenylene-1,4-diyl (unsubstituted, monosubstituted or disubstituted by CN, CH3, CF3, OCF3, unsubstituted, monosubstituted, disubstituted, trisubstituted or tetrasubstituted by F), phenylene-1,3-diyl (unsubstituted, monosubstituted or disubstituted by CN, CH3, CF3, OCF3, unsubstituted, monosubstituted, disubstituted or trisubstituted by F), thiophene-2,5-diyl (unsubstituted or monosubstituted by F), thiophene-2,4-diyl (unsubstituted or monosubstituted by F), 1,3-thiazol-2,5-diyl (unsubstituted or monosubstituted by F), 1,3-thiazol-2,4-diyl (unsubstituted or monosubstituted by F), (1,3,4)-thiadiazol-2,5-diyl, 1,3-dioxane-2,5-diyl (unsubstituted or monosubstituted by CN), tetrahydropyran-2,5-diyl, 6,6-difluorotetra-hydropyran-2,5-diyl, 6,6-difluoro-2,3-dihydro-6H-pyran-2,5-diyl, 6-fluoro-3,4-dihydro-2H-pyran-2,5-diyl, piperidine-1,4-diyl, piperazine-1,4-diyl, pyrimidine-2,5-diyl (unsubstituted or monosubstituted by F), pyridine-2,5-diyl (unsubstituted or monosubstituted by F), 1,2,3,4-tetrahydronaphthalene-2,6-diyl, decaline-2,6-diyl
B2 is cyclohexane-1,4-diyl (unsubstituted, monosubstituted or disubstituted by F, CH3, CN), cyclohex-1-ene-1,4-diyl (unsubstituted or monosubstituted by F), cyclohex-2-ene-1,4-diyl, 1-alkyl-1-silacyclohexane-1,4-diyl, bicyclo[2.2.2]octane-1,4-diyl, phenylene-1,4-diyl (unsubstituted, monosubstituted or disubstituted by CN, CH3, CF3, OCF3, unsubstituted, monosubstituted, disubstituted, trisubstituted or tetrasubstituted by F), phenylene-1,3-diyl (unsubstituted, monosubstituted or disubstituted by CN, CH3, CF3, OCF3, unsubstituted, monosubstituted, disubstituted or trisubstituted by F), thiophene-2,5-diyl, thiophene-2,4-diyl, 1,3-thiazole-2,5-diyl, 1,3-thiazole-2,4-diyl, (1,3,4)-thiadiazole-2,5-diyl, 1,3-dioxane-2,5-diyl (unsubstituted or monosubstituted by CN), tetrahydrofuran-2,5-diyl, tetrahydropyran-2,5-diyl, 6,6-difluorotetrahydropyran-2,5-diyl, 6,6-difluoro-2,3-dihydro-6H-pyran-2,5-diyl, 6-fluoro-3,4-dihydro-2H-pyran-2,5-diyl, pyrimidine-2,5-diyl (unsubstituted or monosubstituted F), pyridine-2,5-diyl (unsubstituted or monosubstituted F), indane-2,6-diyl, piperidine-1,4-diyl, piperazine-1,4-diyl, pyrimidine-2,5-diyl (unsubstituted or monosubstituted by F)
X is xe2x80x94(CH2)nxe2x80x94, where
a) one or two xe2x80x94CH2xe2x80x94 groups may be replaced by xe2x80x94Oxe2x80x94 or xe2x80x94C(xe2x95x90O)xe2x80x94 and/or
b) one xe2x80x94CH2CH2xe2x80x94 group may be replaced by xe2x80x94CHxe2x95x90CHxe2x80x94 and one or more H of the xe2x80x94CH2xe2x80x94 groups may be replaced by F with the provisos that
1) n is 2, 3 or 4
2) two adjacent xe2x80x94CH2xe2x80x94 groups cannot be replaced by xe2x80x94Oxe2x80x94
xe2x80x83a, b, c are each zero, 1 or 2, with the provisos that
1) a must be 1 when R1 is hydrogen, F or CN
2) the sum of a+b+c is at least 1
3) the radicals A and M, respectively, in the brackets may be identical or different when the corresponding index is 2.
Here and hereinbelow, it will be understood that bivalent radicals were designated in the xe2x80x9cfree statexe2x80x9d. This designation is essential for the characterization of the compounds, although strictly in accordance with IUPAC rules, other designations of the bivalent radicals forming part of the entire Markush formulaxe2x80x94meaning incorporation both as image and as mirror imagexe2x80x94would be possible.
According to one embodiment, R1 and R2 are no alkenyl or alkenyloxy radicals.
The active-matrix display is preferably a monostable ferroelectric active-matrix display containing a liquid-crystal layer in the form of a monodomain having an unambiguously defined direction of the layer normal z of the SmC phase, where the layer normal z and the preferential direction n in the nematic or cholesteric phase (N* phase) form an angle of more than 5xc2x0 and the liquid-crystal layer is composed of a ferroelectric (chiral smectic) liquid-crystal mixture comprising at least one compound of the formula (I).
The spontaneous polarization of the liquid-crystal mixture is preferably  less than 200 nC/cm2, particularly preferably  less than 25 nC/cm2, especially  less than 15 nC/cm2, the value DT (15,1), which is defined below, being  greater than 20.
The processes for producing the materials which are suitable for the mixtures of the invention are known in principle, as is the production of liquid-crystal mixtures from the individual components.
For example, the following materials have been described:
thiadiazole derivatives: EP-A-0 309 514; EP-A-0 335 348; U.S. Pat. No. 5,076,961; U.S. Pat. No. 5,200,109
thiazole derivatives: EP-A-0 309 514; EP-A-0 439 170
pyrimidine derivatives: EP-A-0 220 296; 220 297; 227 717; 224 579; 293 910; U.S. Pat. No. 4,891,151; EP-B 0 308 794; U.S. Pat. No. 5,200,521; U.S. Pat. No. 5,370,823; DE-A 43 00 435
4-fluoropyrimidine derivatives: U.S. Pat. No. 5,344,585; EP-A-0 158 137
pyridine derivatives: WO 86/06401; EP-A-0 206 228; EP-A-0 239 403; U.S. Pat. No. 4,795,587; JP-A 07309858; JP-A 62207257; JP-A 05331143; JP-A 05213875; JP-A 04356464; JP-A 01031765; JP-A 08062560; DE-A 40 26 233
fluorinated pyridine derivatives: JP-B 2079059; U.S. Pat. No. 5,389,291; U.S. Pat. No. 5,630,962; U.S. Pat. No. 5,445,763; DE-A 44 27 199; U.S. Pat. No. 5,445,763
2-fluoropyrazine derivatives: U.S. Pat. No. 5,562,859 1,2,3,4-tetrahydroquinazoline derivatives: U.S. Pat. No. 4,402,849; JP-A 08062559; JP-A 08059629; JP-A 07207267
quinoline derivatives: DE-A 195.38 404
dioxane derivatives: Flxc3xcssige Kristalle in Tabellen II (liquid crystals in tables II), pp. 349-352; DD 249 277; DD 249 278; DD 249 279
isoxazole derivatives: Mol. Cryst. Liq. Cryst. 1993, 225, 175-182
pyrane derivatives: JP-A 10168076; JP-A 10176168
naphthalene derivatives: Flxc3xcssige Kristalle in Tabellen II (liquid crystals in tables II) pp. 313-322; DE-A 195 17 056; DE-A 195 17 038; DE-A 195 70 60; DE-A 195 22 167; DE-A 196 52 247; WO 92/16500; EP-A-0 302 875
indane derivatives: EP-A-0 546 338
fluorophenyl derivatives: EP-A-0 210 215; GB-A 2,198,743
difluorophenyl derivatives: EP-A-0 210 215; EP-A-0 332 024, 332 025
trifluorophenyl derivatives: EP-A-0 602 596
tetrafluorophenyl derivatives: EP-A-0 110 002; EP-A-0 113 293; EP-A-0 422 996; JP 58188840; JP 59010553; JP 02180869; Mol. Cryst. Liq. Cryst. 127, 413 (1985)
biphenyl and terphenyl derivatives: Flxc3xcssige Kristalle in Tabellen II (liquid crystals in table II) pp. 269-304; EP-A-0 213 841; EP-A-0 263 843; GB-B 2,198,743; GB-B 2,200,912; EP-B-0 395 666; EP-B-0 332 006; EP-A-0 360 042
bicyclo[2.2.2]octane derivatives: Flxc3xcssige Kristalle in Tabellen II (liquid crystals in table II) pp. 85-95
cyclohexane derivatives: Flxc3xcssige Kristalle in Tabellen II (liquid crystals in table II) pp. 32-72; Landolt-Bxc3x6rnstein Vol. IV/7a, pp. 160-176; DE-A 23 44 732; 24 50 088; 24 29 093; 26 36 684; 27 01 591; 27 52 975; DE-A-32 31 707; EP-A 0 233 267; EP-A 0 238 576
cyclohexene derivatives: Flxc3xcssige Kristalle in Tabellen II (liquid crystals in table II) pp. 79-82; U.S. Pat. No. 5,271,864; DE-A 39 30 119
1-alkylsilacyclohexane derivatives: EP-A-0 761 674; 742 222; 732 335; 727 428
meta-substituted mesogens: U.S. Pat. No. 5,447,656
thiophene derivatives: Flxc3xcssige Kristalle in Tabellen II (liquid crystals in tables II) pp. 353-356; EP-A-0 458 347; EP-A-0 364 923; EP-A-0 392 510; EP-A-0 459 406
benzothiazole derivatives: JP-A 09059266
phenanthrene derivatives: U.S. Pat. No. 5,648,021; EP-B 0 743 971; DE-A 195 24 230; DE-A 197 48 819; DE-A 196 53 010; DE-A 196 53 009; DE-A 196 53 008
fluorene derivatives: Landolt-Bxc3x6rnstein Vol. IV/7a, pp. 36-41; DE-A 197 20 289
ethyne derivatives: U.S. Pat. No. 5,626,792; 5,178,791; 5,457,235; JP 10195025; WO 98 23637; JP 10130188; JP 10120600; EP-A-0 799 878
ethane derivatives: WO 98 23583; WO 98 23563; JP 10147544; JP 09235550; JP 0914660; JP 09087210; JP 06056703; DE-A 42 38 377; JP 06025030; DE-A 32 01 721
and compounds containing the structural elements
silylalkyl: EP-B-0 366 561
cyclopropylalkyl: EP-B-0 318 423/398 155
perfluoroalkyl: Ferroelectrics 1988, 85, 375-384 or U.S. Pat. Nos. 4,886,619, 5,082,587, 5,254,747, 5,262,082, 5,437,812 or 5,482,650
perfluorocyclohexyl: DE-A 197 48 818
(x-fluorocarbonyloxy: Liquid Crystals 1997, vol. 23, no. 5, pp. 659-666
2,3-difluoroalkyloxy: U.S. Pat. No. 5,051,506
2-fluoroalkyloxy: U.S. Pat. No. 4,798,680
(x-chlorocarbonyloxy: U.S. Pat. No. 4,855,429
methyl-branched alkyl chains: EP-B-0 201 578, 211 030; DE-A 196 27 899
containing only one Pendant group: EP-A-0 541 081; EP-A-0 606 090
propionyloxy: DD 284 894; EP-A-0 552 658; GB-B 2,235,192
tetrahydrofuranoyloxy: EP-A-0 355 561
cyanoalkyl: EP-A-0 310 620; EP-A-0 333 760; WO 89/05792
containing an oxirane group: EP-B-0 263 437; EP-B-0 292 954; EP-B-0 365 820; DE-A 4133710; JP-B 2089393; JP-B 3-512741
containing a 1,3-dioxolane group: EP-B-0 288 813; EP-B-0 361 272; EP-B-0 462 156; EP-B-0 351 746
It has been found in accordance with the invention that active-matrix displays in which the ferroelectric smectic phase is stable over a broad temperature range are obtainable by using the compounds of the formula (I). Furthermore, the acute angle is very stable over a broad temperature range, i.e. it is only subject to very small changes. The same applies to the layer leaning angle.
In formula (I), X is preferably xe2x80x94OC(xe2x95x90O)xe2x80x94, xe2x80x94OCH2xe2x80x94 or xe2x80x94OC(xe2x95x90O)CH2CH2xe2x80x94, particularly preferably xe2x80x94OC(xe2x95x90O).
B1 is preferably cyclohexane-1,4-diyl, cyclohex-1-ene-1,4-diyl, phenylene-1,4-diyl, unsubstituted, monosubstituted or disubstituted by F, or thiophene-2,5-diyl, particularly preferably cyclohexane-1,4-diyl or thiophene-2,5-diyl.
A1 is preferably pyrimidine-2,5-diyl (unsubstituted or monosubstituted by F), pyridine-2,5-diyl (unsubstituted or monosubstituted by F), phenylene-1,4-diyl (unsubstituted, monosubstituted or disubstituted by F) or (1,3,4)-thiadiazole-2,5-diyl.
Preferred compounds of the formula (I) correspond to the formulae 
where R1, R2 are as defined above and 
is a bivalent radical selected from the group consisting of phenylene-1,4-diyl, unsubstituted, monosubstituted or disubstituted by F, pyrimidine-2,5-diyl, unsubstituted or monosubstituted by F, pyridine-2,5-diyl, unsubstituted or monosubstituted by F, (1,3,4)-thiadiazole-2,5-diyl, indane-2,5-diyl, cyclohexane-1,4-diyl, unsubstituted or monosubstituted by F or CN, cyclohex-1-ene-1,4-diyl, 1,2,3,4-tetrahydroquinazoline-2,6-diyl 
is a bivalent radical selected from the group consisting of phenylene-1,4-diyl, unsubstituted, monosubstituted or disubstituted by F, pyrimidine-2,5-diyl, unsubstituted or monosubstituted by F, pyridine-2,5-diyl, unsubstituted or monosubstituted by F, indane-2,5-diyl 
is a bivalent radical selected from the group consisting of cyclohexane-1,4-diyl, unsubstituted or monosubstituted by F or CN, cyclohex-1-ene-1,4-diyl, (1,3)-dioxane-2,5-diyl, unsubstituted or monosubstituted by CN, thiophene-2,5-diyl, thiophene-2,4-diyl, phenylene-1,4-diyl, unsubstituted, monosubstituted or disubstituted by F, phenylene-1,3-diyl, unsubstituted, monosubstituted or disubstituted by F.
Particularly preferred compounds of the formula (I) correspond to the formulae 
is a bivalent radical selected from the group consisting of phenylene-1,4-diyl, unsubstituted, monosubstituted or disubstituted by F, (1,3,4)-thiadiazol-2,5-diyl, pyrimidine-2,5-diyl, unsubstituted or substituted by F, pyridine-2,5-diyl, unsubstituted or substituted by F ortho to the nitrogen atom, 1,2,3,4-tetrahydroquinazoline-2,6-diyl 
is a bivalent radical selected from the group consisting of phenylene-1,4-diyl, unsubstituted, monosubstituted or disubstituted by F, pyrimidine-2,5-diyl, unsubstituted or monosubstituted by F, pyridine-2,5-diyl, unsubstituted or monosubstituted by F 
is a bivalent radical selected from the group consisting of cyclohexane-1,4-diyl, thiophene-2,5-diyl, phenylene-1,4-diyl and R8, R9 are each, independently of one another, hydrogen or a straight-chain or branched alkyl or alkoxy radical having 1 to 16 carbon atoms, where one or two nonterminal xe2x80x94CH2xe2x80x94 groups maybe replaced by xe2x80x94Oxe2x80x94 or xe2x80x94C(xe2x95x90O)xe2x80x94 or xe2x80x94CHxe2x95x90CHxe2x80x94 with the provisos that R8 and R9 cannot both be hydrogen and that two adjacent xe2x80x94CH2xe2x80x94 groups cannot be replaced by xe2x80x94Oxe2x80x94.
Very particularly preferred compounds correspond to the formulae 
If desired, the formulae (Ia1ac) to (Ia1ak) above can also be excluded.
The liquid-crystal mixture of the display according to the invention preferably comprises, in addition to one or more compounds of the formula (I), 2 to 30 additional compounds selected as one or more representatives form the substance classes of the groups (II) to (XVII) 
where:
R10, R11 are as defined for R1, R2 where additionally the terminal xe2x80x94CH3xe2x80x94 group may in each case be replaced by one of the chiral groups (optically active or racemic) below: 
xe2x80x83R3, R4, R5, R6, R7 are identical or different and are each
a) hydrogen
b) a straight-chain or branched alkyl radical (with or without asymmetric carbon atoms) having 1 to 16 carbon atoms, where
b1) one or more nonadjacent and nonterminal CH2 groups may be replaced by xe2x80x94Oxe2x80x94 and/or
b2) one or two CH2 groups may be replaced by xe2x80x94CHxe2x95x90CHxe2x80x94,
c) R4 and R5 together may alternatively be xe2x80x94(CH2)4xe2x80x94 or xe2x80x94(CH2)5xe2x80x94 if they are attached to an oxirane, dioxolane, tetrahydrofuran, tetrahydropyran, butyrolactone or valerolactone system;
R12 is hydrogen or a straight-chain or branched alkyl radical (with or without asymmetric carbon atoms) having 1 to 16 carbon atoms, where one or more H may be replaced by F and one or two nonadjacent nonterminal xe2x80x94CH2xe2x80x94 groups may be replaced by xe2x80x94Oxe2x80x94
Z1, Z2, Z3, Z4, Z5, Z6 are each, independently of one another, H or F 
xe2x80x83is a bivalent radical selected from the group consisting of pyridine-2,5-diyl, unsubstituted or monosubstituted by F, pyrimidine-2,5-diyl, unsubstituted or monosubstituted by F, pyrazine-2,5-diyl, unsubstituted or monosubstituted by F, 
xe2x80x83is a bivalent radical selected from the group consisting of naphthalene-2,6-diyl, in which one or two ring carbon atoms may be replaced by N and which can be monosubstituted or disubstituted by F or CN and in which D1 or D2 may also be a (saturated) alicycle 
xe2x80x83is a bivalent radical selected from the group consisting of phenylene-1,4-diyl, unsubstituted, monosubstituted or disubstituted by CN, or unsubstituted, monosubstituted, disubstituted, trisubstituted or tetrasubstituted by F, pyridine-2,5-diyl, unsubstituted or monosubstituted by F, pyrimidine-2,5-diyl, unsubstituted or monosubstituted by F, cyclohexane-1,4-diyl 
xe2x80x83is a bivalent radical selected from the group consisting of indane-2,5-diyl, unsubstituted, monosubstituted or disubstituted by F in the aromatic ring, indan-1-one-2,6-diyl, unsubstituted, monosubstituted or disubstituted by F in the aromatic ring, benzothiazole-2,6-diyl, benzothiazole-2,5-diyl, benzo[b]thiophene-2,5-diyl, benzo[b]thiophene-2,6-diyl 
xe2x80x83is a bivalent radical selected from the group consisting of (1,3,4)-thiadiazole-2,5-diyl, (1,3)-thiazole-2,5-diyl, thiophene-2,5-diyl, (1,3,4)-oxadiazole-2,5-diyl, (1,3)-oxazole-2,5-diyl, isoxazole-2,5-diyl 
xe2x80x83is a bivalent radical selected from the group consisting of 1,1xe2x80x2-biphenyl-4,4xe2x80x2-diyl, unsubstituted, monosubstituted or disubstituted by CN, or unsubstituted, monosubstituted, disubstituted, trisubstituted or tetrasubstituted by F, 1,1xe2x80x2-phenylcyclohexyl-4,4xe2x80x2-diyl, 5,5xe2x80x2-pyridylpyrimidine-2,2xe2x80x2-diyl, unsubstituted or monosubstituted by F in one or both of the heterocycles, 5,2xe2x80x2-pyridylpyrimidine-2,5xe2x80x2-diyl, unsubstituted or monosubstituted by F in one or both of the heterocycles, 1,2xe2x80x2-phenyldioxane-4,5xe2x80x2-diyl, 1,2xe2x80x2-(2-fluorophenyl)dioxane-4,5xe2x80x2-diyl, 1,2xe2x80x2-(3-fluorophenyl)dioxane-4,5xe2x80x2-diyl, 1,2xe2x80x2-(2,3-difluorophenyl)dioxane-4,5xe2x80x2-diyl 
xe2x80x83is a bivalent phenanthrene-2,7-diyl radical in which one or two ring carbon atoms may be replaced by N and which may be monosubstituted, disubstituted, trisubstituted or tetrasubstituted by F and in which P and/or P may be a (saturated) alicycle 
xe2x80x83is a bivalent fluorene-2,7-diyl radical in which the xe2x80x94CH2xe2x80x94 group in U2 may be replaced by xe2x80x94C(xe2x95x90O)xe2x80x94, xe2x80x94CHFxe2x80x94 or xe2x80x94CF2xe2x80x94 
xe2x80x83is a bivalent radical selected from the group consisting of phenylene-1,3-diyl, unsubstituted, monosubstituted or disubstituted by F, cyclohexane-1,3-diyl, unsubstituted or monosubstituted by F or CN, pyridine-2,6-diyl, pyridine-2,4-diyl, pyridine-3,5-diyl, pyridine-4,6-diyl, pyrimidine-4,6-diyl, 
xe2x80x83is a bivalent radical selected from the group consisting of cyclohexane-1,4-diyl, unsubstituted or monosubstituted by CN, CH3, or disubstituted by F, cyclohex-1-ene-1,4-diyl, perfluorocyclohexane-1,4-diyl, cyclohex-2-ene-1,4-diyl, 1-alkyl-1-silacyclohexane-1,4-diyl, bicyclo[2.2.2]-octane-1,4-diyl. 
xe2x80x83is a bivalent radical selected from the group consisting of phenylene-1,4-diyl, unsubstituted, monosubstituted or disubstituted by CN or F, naphthalene-2,6-diyl, in which one or two ring carbon atoms may be replaced by N and which may be monosubstituted or disubstituted by CN or F, cyclohexane-1,4-diyl, cyclohex-1-ene-1,4-diyl, bicyclo[2.2.2]octane-1,4-diyl, (1,3)-dioxane-2,5-diyl, pyridine-2,5-diyl, unsubstituted or monosubstituted by F, pyrimidine-2,5-diyl, unsubstituted or monosubstituted by F, (1,3,4)-thiadiazole-2,5-diyl, indane-2,5-diyl, unsubstituted, monosubstituted or disubstituted by F in the aromatic ring, thiophene-2,5-diyl 
xe2x80x83is a bivalent radical selected from the group consisting of phenylene-1,4-diyl, unsubstituted, monosubstituted or disubstituted by CN or F, naphthalene-2,6-diyl, in which one or two ring carbon atoms may be replaced by N and which may be monosubstituted or disubstituted by CN or F, cyclohexane-1,4-diyl, cyclohex-1-ene-1,4-diyl, bicyclo[2.2.2]octane-1,4-diyl, (1,3)-dioxane-2,5-diyl, indane-2,5-diyl, unsubstituted, monosubstituted or disubstituted by F in the aromatic ring, thiophene-2,5-diyl
p, q, s are each zero or 1
r is 1 or 2.
The following meanings are preferred:
in (II), 
is a bivalent radical selected from the group of pyridine-2,5-diyl, unsubstituted or monosubstituted by F, pyrimidine-2,5-diyl, unsubstituted or monosubstituted by F
Z1, Z2 are both H or both F
R10, R11 are, independently of one another, identical or different and are each hydrogen or a straight-chain or branched alkyl or alkyloxy radical (with or without asymmetric carbon atoms) having 2-16 carbon atoms, where one or two nonterminal xe2x80x94CH2xe2x80x94 groups may be replaced by xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94OC(xe2x95x90O)xe2x80x94, xe2x80x94C(xe2x95x90O)Oxe2x80x94 and one or more H atoms may be replaced by F with the proviso that only one of the radicals R10, R11 can be hydrogen
in (III), 
is a bivalent radical selected from the group consisting of pyridine-2,5-diyl, unsubstituted or monosubstituted by F, pyrimidine-2,5-diyl, unsubstituted or monosubstituted by F 
is a bivalent radical selected from the group consisting of cyclohexane-1,4-diyl, unsubstituted or monosubstituted by CN, cyclohex-1-ene-1,4-diyl, cyclohex-2-ene-1,4-diyl,
Z1, Z2 are both H or both F,
in (IV), 
is a bivalent radical selected from the group consisting of pyridine-2,5-diyl, unsubstituted or monosubstituted by F, pyrimidine-2,5-diyl, unsubstituted or monosubstituted by F
Z1, Z2 are both H or both F,
Z3, Z4 are both H or both F
in (V), 
is a bivalent radical selected from the group consisting of pyridine-2,5-diyl, unsubstituted or monosubstituted by F, pyrimidine-2,5-diyl, unsubstituted or monosubstituted by F
Z1, Z2 are both H or both F,
Z3, Z4 are both H or F, with the proviso that Z1, Z2 and Z3, Z4 are not simultaneously F
in (VI)
Z1, Z2, Z3, Z4, Z5, Z6 one element of this group is F or (Z1 and Z2) or (Z3 and Z4) are both F
in (VII),
Z1 and Z2 are both H or both F; Z3 and Z4 are both H
in (VIII) 
is a bivalent radical selected from the group consisting of pyridine-2,5-diyl, unsubstituted or monosubstituted by F, pyrimidine-2,5-diyl, unsubstituted or monosubstituted by F 
is a bivalent radical selected from the group consisting of phenylene-1,4-diyl, unsubstituted, monosubstituted or disubstituted by F, naphthalene-2,6-diyl, unsubstituted, monosubstituted or disubstituted by F, cyclohexane-1,4-diyl
p, q, s are each zero or 1; their sum is zero or 1
in (IX), 
is naphthalene-2,6-diyl which can be monosubstituted or disubstituted by F 
is a bivalent radical selected from the group consisting of phenylene-1,4-diyl, unsubstituted, monosubstituted or disubstituted by F, pyridine-2,5-diyl, unsubstituted or monosubstituted by F, pyrimidine-2,5-diyl, unsubstituted or monosubstituted by F
in (X), 
is a bivalent radical selected from the group consisting of indane-2,5-diyl, unsubstituted, monosubstituted or disubstituted by F in the aromatic ring, indan-1-one-2,6-diyl, and possibly benzothiazole-2,6-diyl 
is a bivalent radical selected from the group consisting of phenylene-1,4-diyl, unsubstituted, monosubstituted or disubstituted by F, pyridine-2,5-diyl, unsubstituted or monosubstituted by F, pyrimidine-2,5-diyl, unsubstituted or monosubstituted by F
p is 1
q is zero
in (IX), 
is (1,3,4)-thiadiazole-2,5-diyl 
is a bivalent radical selected from the group consisting of phenylene-1,4-diyl, unsubstituted, monosubstituted or disubstituted by F, pyridine-2,5-diyl, unsubstituted or monosubstituted by F, pyrimidine-2,5-diyl, unsubstituted or monosubstituted by F, cyclohexane-1,4-diyl
p is zero or 1
q is zero or 1, with the proviso that q is zero when p is 1
in (XII), 
is a bivalent radical selected from the group consisting of 1,1xe2x80x2-biphenyl-4,4xe2x80x2-diyl, unsubstituted, monosubstituted or disubstituted by F, 1,1xe2x80x2-phenylcyclohexyl-4,4xe2x80x2-diyl, 5,5xe2x80x2-pyridylpyrimidine-2,2xe2x80x2-diyl, unsubstituted or monosubstituted by F in one or both of the heterocycles, 5,2xe2x80x2-pyridylpyrimidine-2,5xe2x80x2-diyl, unsubstituted or monosubstituted by F in one or both of the heterocycles
in (XIII), 
is a bivalent phenanthrene-2,7-diyl radical in which one or two ring carbon atoms may also be replaced by N and which may be monosubstituted or disubstituted by F and in which P2 can be a (saturated) alicycle
p is zero
in (XIV), 
is a bivalent fluorene-2,7-diyl radical 
is a phenylene-2,4-diyl radical
is zero or 1
in (XV), 
is a bivalent radical selected from the group consisting of phenylene-1,4-diyl, unsubstituted, monosubstituted or disubstituted by F, pyridine-2,5-diyl, unsubstituted or monosubstituted by F, pyrimidine-2,5-diyl, unsubstituted or monosubstituted by F 
is a bivalent radical selected from the group consisting of phenylene-1,3-diyl, unsubstituted, monosubstituted or disubstituted by F
p is zero or 1
in (XVI), 
is a bivalent radical selected from the group consisting of phenylene-1,4-diyl, unsubstituted, monosubstituted or disubstituted by F, naphthalene-2,6-diyl, unsubstituted, monosubstituted or disubstituted by F 
is a bivalent radical selected from the group consisting of phenylene-1,4-diyl, unsubstituted, monosubstituted or disubstituted by F, naphthalene-2,6-diyl, unsubstituted, monosubstituted or disubstituted by F, cyclohexane-1,4-diyl, pyridine-2,5-diyl, unsubstituted or monosubstituted by F, pyrimidine-2,5-diyl, unsubstituted or monosubstituted by F
r is 1
q, s are each zero or 1, their sum being 1
in (XVII), 
is a bivalent radical selected from the group consisting of phenylene-1,4-diyl, unsubstituted, monosubstituted or disubstituted by F, naphthalene-2,6-diyl, unsubstituted, monosubstituted or disubstituted by F, cyclohexane-1,4-diyl, pyridine-2,5-diyl, unsubstituted or monosubstituted by F, pyrimidine-2,5-diyl, unsubstituted or monosubstituted by F, (1,3,4)-thiadiazole-2,5-diyl, indane-2,5-diyl 
is a bivalent radical selected from the group consisting of phenylene-1,4-diyl, unsubstituted, monosubstituted or disubstituted by F, naphthalene-2,6-diyl, unsubstituted, monosubstituted or disubstituted by F, cyclohexane-1,4-diyl, cyclohex-1-ene-1,4-diyl, bicyclo-[2.2.2]octane-1,4-diyl, (1,3)-dioxane-2,5-diyl, pyridine-2,5-diyl, unsubstituted or monosubstituted by F, pyrimidine-2,5-diyl, unsubstituted or monosubstituted by F, (1,3,4)-thiadiazol-2,5-diyl, indane-2,5-diyl, unsubstituted, monosubstituted or disubstituted by F in the aromatic ring, thiophene-2,5-diyl
q, s are each zero or 1; their sum being 0 or 1.
Particular preference is given to the following meanings:
in (II), 
is pyridine-2,5-diyl, 2-fluoropyridine-3,6-diyl or pyrimidine-2,5-diyl
Z1, Z2 are both H or both F
R10, R11 are, independently of one another, identical or different and are each hydrogen or a straight-chain or branched alkyl or alkyloxy radical (with or without asymmetric carbon atoms) having 2-16 carbon atoms, where one or two nonterminal xe2x80x94CH2xe2x80x94 groups may be replaced by xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94OC(xe2x95x90O)xe2x80x94, xe2x80x94C(xe2x95x90O)Oxe2x80x94 and one or more H atoms may be replaced by F with the proviso that only one of the radicals R10, R11 can be hydrogen
In (III), 
is a bivalent radical selected from the group consisting of pyridine-2,5-diyl, 2-fluoropyridine-3,6-diyl, pyrimidine-2,5-diyl, 
is cyclohexane-1,4-diyl,
Z1, Z2 are both H or both F,
R10, R11 are, independently of one another, identical of different and are each hydrogen or a straight-chain or branched alkyl or alkyloxy radical (with or without asymmetric carbon atoms) having 2-16 carbon atoms, where one or two nonterminal xe2x80x94CH2xe2x80x94 groups maybe replaced by xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94OC(xe2x95x90O)xe2x80x94, xe2x80x94C(xe2x95x90O)Oxe2x80x94 and one or more H atoms may be replaced by F with the proviso that only one of the radicals R10, R11 can be hydrogen.
In (IV), 
is pyridine-2,5-diyl, 2-fluoropyridine-3,6-diyl, pyrimidine-2,5-diyl,
Z1, Z2, Z3, Z4 are each H
R10, R11 are, independently of one another, identical or different and are each hydrogen or a straight-chain or branched alkyl or alkyloxy radical (with or without asymmetric carbon atoms) having 2-16 carbon atoms, where one or two nonterminal xe2x80x94CH2xe2x80x94 groups may be replaced by xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94OC(xe2x95x90O)xe2x80x94, xe2x80x94C(xe2x95x90O)Oxe2x80x94 and one or more H atoms may be replaced by F with the proviso that only one of the radicals R10, R11 can be hydrogen.
In (V), 
is pyridine-2,5-diyl, 2-fluoropyridine-3,6-diyl, pyrimidine-2,5-diyl,
Z1, Z2, Z3, Z4 are each H
R10, R11 are, independently of one another, identical or different and are each hydrogen or a straight-chain or branched alkyl or alkyloxy radical (with or without asymmetric carbon atoms) having 2-16 carbon atoms, where one or two nonterminal xe2x80x94CH2xe2x80x94 groups may be replaced by xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94OC(xe2x95x90O)xe2x80x94, xe2x80x94C(xe2x95x90O)Oxe2x80x94 and one or more H atoms may be replaced by F with the proviso that only one of the radicals R10, R11 can be hydrogen.
In (VI)
Z1, Z2, Z3, Z4, Z5, Z6 one element of this group is F or
Z1 and Z2=F, Z3, Z4, Z5, Z6=H
Z3 and Z4=F, Z1, Z2, Z5, Z6=H
R10, R11 are, independently of one another, identical or different and are each hydrogen or a straight-chain or branched alkyl or alkyloxy radical (with or without asymmetric carbon atoms) having 2-16 carbon atoms, where one or two nonterminal xe2x80x94CH2xe2x80x94 groups may be replaced by xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94OC(xe2x95x90O)xe2x80x94, xe2x80x94C(xe2x95x90O)Oxe2x80x94 and one or more H atoms may be replaced by F with the proviso that only one of the radicals R10, R11 can be hydrogen.
In (VII),
Z1 and Z2 are both F; Z3 and Z4 are both H
R10, R11 are, independently of one another, identical or different and are each hydrogen or a straight-chain or branched alkyl or alkyloxy radical (with or without asymmetric carbon atoms) having 2-16 carbon atoms, where one or two nonterminal xe2x80x94CH2xe2x80x94 groups may be replaced by xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94OC(xe2x95x90O)xe2x80x94, xe2x80x94C(xe2x95x90O)Oxe2x80x94 and one or more H atoms may be replaced by F with the proviso that only one of the radicals R10, R11 can be hydrogen.
In (VIII), 
is pyridine-2,5-diyl, pyrimidine-2,5-diyl 
is phenylene-1,4-diyl, unsubstituted, monosubstituted or disubstituted by F,
p, q, s are each zero or 1; their sum being zero or 1
R10, R11 are, independently of one another, identical or different and are each hydrogen or a straight-chain or branched alkyl or alkyloxy radical (with or without asymmetric carbon atoms) having 2-16 carbon atoms, where one or two nonterminal xe2x80x94CH2xe2x80x94 groups may be replaced by xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94OC(xe2x95x90O)xe2x80x94, xe2x80x94C(xe2x95x90O)Oxe2x80x94 and one or more H atoms may be replaced by F with the proviso that only one of the radicals R10, R11 can be hydrogen.
In (IX), 
is naphthalene-2,6-diyl or 1-fluoronaphthalene-2,6-diyl 
is phenylene-1,4-diyl, unsubstituted, monosubstituted or disubstituted by F, pyridine-2,5-diyl, 2-fluoropyridine-3,6-diyl, pyrimidine-2,5-diyl
R10, R11 are, independently of one another, identical or different and are each hydrogen or a straight-chain or branched alkyl or alkyloxy radical (with or without asymmetric carbon atoms) having 2-16 carbon atoms, where one or two nonterminal xe2x80x94CH2xe2x80x94 groups may be replaced by xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94OC(xe2x95x90O)xe2x80x94, xe2x80x94C(xe2x95x90O)Oxe2x80x94 and one or more H atoms may be replaced by F with the proviso that only one of the radicals R10, R11 can be hydrogen.
In (X), 
is benzothiazole-2,6-diyl, possibly also indane-2,5-diyl 
is phenylene-1,4-diyl, pyridine-2,5-diyl, pyrimidine-2,5-diyl
p is 1
q is zero
R10, R11 are, independently of one another, identical or different and are each hydrogen or a straight-chain or branched alkyl or alkyloxy radical (with or without asymmetric carbon atoms) having 2-16 carbon atoms, where one or two nonterminal xe2x80x94CH2xe2x80x94 groups may be replaced by xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94OC(xe2x95x90O)xe2x80x94, xe2x80x94C(xe2x95x90O)Oxe2x80x94 and one or more H atoms may be replaced by F with the proviso that only one of the radicals R10, R11 can be hydrogen.
In (IX), 
is (1,3,4)-thiadiazole-2,5-diyl 
is phenylene-1,4-diyl, pyridine-2,5-diyl, cyclohexane-1,4-diyl
p is zero or 1
q is zero or 1, with the proviso that q is zero when p is 1
R10, R11 are, independently of one another, identical or different and are each hydrogen or a straight-chain or branched alkyl or alkyloxy radical (with or without asymmetric carbon atoms) having 2-16 carbon atoms, where one or two nonterminal xe2x80x94CH2xe2x80x94 groups may be replaced by xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94OC(xe2x95x90O)xe2x80x94, xe2x80x94C(xe2x95x90O)Oxe2x80x94 and one or more H atoms may be replaced by F with the proviso that only one of the radicals R10, R11 can be hydrogen.
In (XII), 
is a bivalent radical selected from the group consisting of 1,1xe2x80x2-biphenyl-4,4xe2x80x2-diyl, unsubstituted, monosubstituted or disubstituted by F, 1,1xe2x80x2-phenylcyclohexyl-4,4xe2x80x2-diyl,
R10, R11 are, independently of one another, identical or different and are each hydrogen or a straight-chain or branched alkyl or alkyloxy radical (with or without asymmetric carbon atoms) having 2-16 carbon atoms, where one or two nonterminal xe2x80x94CH2xe2x80x94 groups may be replaced by xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94OC(xe2x95x90O)xe2x80x94, xe2x80x94C(xe2x95x90O)Oxe2x80x94 and one or more H atoms may be replaced by F with the proviso that only one of the radicals R10, R11 can be hydrogen.
In (XIII), 
is phenanthrene-2,7-diyl, 1-fluorophenanthrene-2,7-diyl or 1,8-difluorophenanthrene-2,7-diyl, in which P2 may alternatively be a (saturated) alicycle
R10, R11 are, independently of one another, identical or different and are each hydrogen or a straight-chain or branched alkyl or alkyloxy radical (with or without asymmetric carbon atoms) having 2-16 carbon atoms, where one or two nonterminal xe2x80x94CH2xe2x80x94 groups may be replaced by xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94OC(xe2x95x90O)xe2x80x94, xe2x80x94C(xe2x95x90O)Oxe2x80x94 and one or more H atoms may be replaced by F with the proviso that only one of the radicals R10, R11 can be hydrogen
p is zero.
In (XIV), 
is a bivalent fluorene-2,7-diyl radical 
is a phenylene-2,4-diyl radical
p is zero or 1
R10, R11 are, independently of one another, identical or different and are each hydrogen or a straight-chain or branched alkyl or alkyloxy radical (with or without asymmetric carbon atoms) having 2-16 carbon atoms, where one or two nonterminal xe2x80x94CH2xe2x80x94 groups may be replaced by xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94OC(xe2x95x90O)xe2x80x94, xe2x80x94C(xe2x95x90O)Oxe2x80x94 and one or more H atoms may be replaced by F with the proviso that only one of the radicals R10, R11 can be hydrogen.
In (XV), 
is phenylene-1,4-diyl, pyridine-2,5-diyl, pyrimidine-2,5-diyl, 
is phenylene-1,3-diyl
p is 1
R10, R11 are, independently of one another, identical or different and are each hydrogen or a straight-chain or branched alkyl or alkyloxy radical (with or without asymmetric carbon atoms) having 2-16 carbon atoms, where one or two nonterminal xe2x80x94CH2xe2x80x94 groups may be replaced by xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94OC(xe2x95x90O)xe2x80x94, xe2x80x94C(xe2x95x90O)Oxe2x80x94 and one or more H atoms may be replaced by F with the proviso that only one of the radicals R10, R11 can be hydrogen.
In (XVI), 
is phenylene-1,4-diyl, unsubstituted, monosubstituted or disubstituted by F, naphthalene-2,6-diyl, unsubstituted, monosubstituted or disubstituted by F 
is phenylene-1,4-diyl, unsubstituted, monosubstituted or disubstituted by F, cyclohexane-1,4-diyl, pyridine-2,5-diyl, 2-fluoropyridine-3,6-diyl, pyrimidine-2,5-diyl
r is 1
q, s are each zero or 1, their sum being 1
R10, R11 are, independently of one another, identical or different and are each hydrogen or a straight-chain or branched alkyl or alkyloxy radical (with or without asymmetric carbon atoms) having 2-16 carbon atoms, where one or two nonterminal xe2x80x94CH2xe2x80x94 groups may be replaced by xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94OC(xe2x95x90O)xe2x80x94, xe2x80x94C(xe2x95x90O)Oxe2x80x94 and one or more H atoms may be replaced by F with the proviso that only one of the radicals R10, R11 can be hydrogen.
In (XVII), 
is phenylene-1,4-diyl, unsubstituted, monosubstituted or disubstituted by F, cyclohexane-1,4-diyl, pyridine-2,5-diyl, pyrimidine-2,5-diyl, (1,3,4)-thiadiazole-2,5-diyl 
is phenylene-1,4-diyl, unsubstituted, monosubstituted or disubstituted by F, cyclohexane-1,4-diyl, pyridine-2,5-diyl, 2-fluoropyridine-3,6-diyl, pyrimidine-2,5-diyl, (1,3,4)-thiadiazole-2,5-diyl q, s are each zero or 1; their sum being 0 or 1
R10, R11 are, independently of one another, identical or different and are each hydrogen or a straight-chain or branched alkyl or alkyloxy radical (with or without asymmetric carbon atoms) having 2-16 carbon atoms, where one or two nonterminal xe2x80x94CH2xe2x80x94 groups may be replaced by xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94OC(xe2x95x90O)xe2x80x94, xe2x80x94C(xe2x95x90O)Oxe2x80x94 and one or more H atoms may be replaced by F with the proviso that only one of the radicals R10, R11 can be hydrogen.
The liquid-crystal mixture preferably consists of 3-30 compounds and comprises at least one compound of the formula (I) and at least one compound of the formula (II) and, if desired, at least one compound of the formula (III).
Preferably, the liquid-crystal mixture additionally comprises at least one compound selected from the groups (IV), (V), (VI), (VII).
Particularly preferably, the liquid-crystal mixture additionally comprises at least one compound selected from the groups (VIII), (IX), (XII), (XVI), (XVII). Likewise particularly preferably, the liquid-crystal mixture additionally comprises at least one compound selected from the groups (X), (XI), (XIV), (XV).
The liquid-crystal mixture may also comprise at least one compound of the formula (XIII).
Preferably, the mixture additionally comprises at least one compound selected from the group (I) to (XVII), where
R10, R11 are, independently of one another, identical or different and are each hydrogen or a straight-chain or branched alkyl or alkyloxy radical (with or without asymmetric carbon atoms) having 2-16 carbon atoms, where one or two nonterminal xe2x80x94CH2xe2x80x94 groups may be replaced by xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94OC(xe2x95x90O)xe2x80x94, xe2x80x94C(xe2x95x90O)Oxe2x80x94 and one or more H atoms may be replaced by F with the proviso that only one of the radicals R10, R11 can be hydrogen and where, in addition, the terminal xe2x80x94CH3xe2x80x94 group in at least one of R10, R11 is replaced by one of the following chiral groups (optically active): 
xe2x80x83R3, R4, R5, R6, R7 are identical or different and are each
a) hydrogen
b) a straight-chain or branched alkyl radical (with or without asymmetric carbon atoms) having 1 to 16 carbon atoms, where
b1) one or more nonadjacent and nonterminal CH2 groups may be replaced by xe2x80x94Oxe2x80x94 and/or
b2) one or two CH2 groups may be replaced by xe2x80x94CHxe2x95x90CHxe2x80x94,
c) R4 and R5 together may alternatively be xe2x80x94(CH2)4xe2x80x94 or xe2x80x94(CH2)5xe2x80x94 if they are attached to an oxirane, dioxolane, tetrahydrofuran, tetrahydropyran, butyrolactone or valerolactone system.
Particularly preferably, the mixture comprises 1 to 5 compounds selected from the group (I) to (XVII), where
R10, R11 are, independently of one another, identical or different and are each hydrogen or a straight-chain or branched alkyl or alkyloxy radical (with or without asymmetric carbon atoms) having 2-16 carbon atoms, where one or two nonterminal xe2x80x94CH2xe2x80x94 groups may be replaced by xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94OC(xe2x95x90O)xe2x80x94, xe2x80x94C(xe2x95x90O)Oxe2x80x94 and one or more H atoms may be replaced by F with the proviso that only one of the radicals R10, R11 can be hydrogen and where, in addition, the terminal xe2x80x94CH3xe2x80x94 group in at least one of R10, R11 is replaced by one of the following chiral groups (optically active): 
R3 is hydrogen or a straight-chain or branched alkyl radical (with or without asymmetric carbon atoms) having 1 to 16 carbon atoms.
Preference is given to liquid-crystal mixtures of the invention which comprise 3 to 25 components, including
1 to 15 compounds of the formula (I)
1 to 15 compounds of the formula (II)
1 to 7 compounds of the formula (III).
Preference is furthermore given to liquid-crystal mixtures of the invention which comprise 3 to 25 components, including
1 to 15 compounds of the formula (I)
1 to 15 compounds of the formula (II)
1 to 7 compounds of the formula (III)
1 to 7 compounds of the formula (IV).
Preference is furthermore given to liquid-crystal mixtures of the invention which comprise 3 to 25 components, including
1 to 15 compounds of the formula (I)
1 to 15 compounds of the formula (II)
1 to 7 compounds of the formula (III)
1 to 7 compounds of the formula (IV)
1 to 7 compounds of the formula (V).
Preference is furthermore given to liquid-crystal mixtures of the invention which comprise 3 to 25 components, including
1 to 15 compounds of the formula (I)
1 to 15 compounds of the formula (II)
1 to 7 compounds of the formula (III)
1 to 7 compounds of the formula (IV)
1 to 7 compounds of the formula (V)
1 to 7 compounds of the formula (VI).
Preference is furthermore given to liquid-crystal mixtures of the invention which comprise 3 to 25 components, including
1 to 15 compounds of the formula (I)
1 to 15 compounds of the formula (II)
1 to 7 compounds of the formula (III)
1 to 7 compounds of the formula (IV)
1 to 7 compounds of the formula (VI)
1 to 7 compounds of the formula (VII).
Preference is furthermore given to liquid-crystal mixtures of the invention which comprise 3 to 25 components, including
1 to 15 compounds of the formula (I)
1 to 15 compounds of the formula (II)
1 to 7 compounds of the formula (III)
1 to 7 compounds of the formula (IV)
1 to 7 compounds of the formula (VI).
Preference is furthermore given to liquid-crystal mixtures of the invention which comprise 3 to 25 components, including
1 to 15 compounds of the formula (I)
1 to 15 compounds of the formula (II)
1 to 7 compounds of the formula (III)
1 to 7 compounds of the formula (IV)
1 to 7 compounds of the formula (VI)
1 to 7 compounds of the formula (XII).
Preference is furthermore given to liquid-crystal mixtures of the invention which comprise 3 to 25 components, including
1 to 15 compounds of the formula (I)
1 to 15 compounds of the formula (II)
1 to 7 compounds of the formula (III)
1 to 7 compounds of the formula (IV)
1 to 7 compounds of the formula (V)
1 to 7 compounds of the formula (VI)
1 to 7 compounds of the formula (VII).
Preference is furthermore given to liquid-crystal mixtures of the invention which comprise 3 to 25 components, including
1 to 15 compounds of the formula (I)
1 to 15 compounds of the formula (II)
1 to 7 compounds of the formula (IV).
Preference is furthermore given to liquid-crystal mixtures of the invention which comprise 3 to 25 components, including
1 to 15 compounds of the formula (I)
1 to 15 compounds of the formula (II)
1 to 7 compounds of the formula (IV)
1 to 7 compounds of the formula (VI).
Preference is furthermore given to liquid-crystal mixtures of the invention which comprise 3 to 25 components, including
1 to 15 compounds of the formula (I)
1 to 15 compounds of the formula (II)
1 to 7 compounds of the formula (IV)
1 to 7 compounds of the formula (XII).
Preference is furthermore given to liquid-crystal mixtures of the invention which comprise 3 to 25 components, including
1 to 15 compounds of the formula (I)
1 to 15 compounds of the formula (II)
1 to 7 compounds of the formula (IV)
1 to 7 compounds of the formula (IX).
Particular preference is given to liquid-crystal mixtures of the invention which comprise 3 to 25 components, including
1 to 12 compounds of the formula (I)
2 to 12 compounds of the formula (II)
1 to 5 compounds of the formula (III).
Particular preference is given to liquid-crystal mixtures of the invention which comprise 3 to 25 components, including
1 to 12 compounds of the formula (I)
2 to 12 compounds of the formula (II)
1 to 5 compounds of the formula (III)
1 to 5 compounds of the formula (IV)
1 to 5 compounds of the formula (VI)
1 to 5 compounds of the formula (VII).
Particular preference is given to liquid-crystal mixtures of the invention which comprise 3 to 25 components, including
1 to 12 compounds of the formula (I)
2 to 12 compounds of the formula (II)
1 to 5 compounds of the formula (III)
1 to 5 compounds of the formula (IV)
1 to 5 compounds of the formula (VI).
Particular preference is given to liquid-crystal mixtures of the invention which comprise 3 to 25 components, including
1 to 12 compounds of the formula (I)
2 to 12 compounds of the formula (II)
1 to 5 compounds of the formula (III)
1 to 5 compounds of the formula (IV)
1 to 5 compounds of the formula (VI)
1 to 5 compounds of the formula (XII).
Particular preference is given to liquid-crystal mixtures of the invention which comprise 3 to 25 components, including
1 to 12 compounds of the formula (I)
2 to 12 compounds of the formula (II)
1 to 5 compounds of the formula (IV).
Particular preference is given to liquid-crystal mixtures of the invention which comprise 3 to 25 components, including
1 to 12 compounds of the formula (I)
2 to 12 compounds of the formula (II)
1 to 5 compounds of the formula (IV)
1 to 5 compounds of the formula (VI).
Particular preference is given to liquid-crystal mixtures of the invention which comprise 3 to 25 components, including
1 to 12 compounds of the formula (I)
2 to 12 compounds of the formula (II)
1 to 5 compounds of the formula (IV)
1 to 5 compounds of the formula (VI)
1 to 5 compounds of the formula (VII).
Very particular preference is given to liquid-crystal mixtures of the invention which comprise 3 to 23 components, including
1 to 8 compounds of the formula (I)
2 to 10 compounds of the formula (II)
1 to 3 compounds of the formula (III).
Very particular preference is furthermore given to liquid-crystal mixtures of the invention which comprise 3 to 23 components, including
1 to 8 compounds of the formula (I)
2 to 10 compounds of the formula (II), in which, in at least one compound, a xe2x80x94CH2-group is replaced by xe2x80x94OC(xe2x95x90O)xe2x80x94
1 to 3 compounds of the formula (III).
According to one embodiment of the invention, very particular preference is furthermore given to mixtures of the invention which comprise 3 to 30 components, including
4 to 8 compounds of the formula (I)
1 to 10 compounds of the formula (II)
1 to 4 compounds of the formula (VI)
1 to 4 compounds of the formula (X)
1 to 4 compounds of the formula (XI).
In a particular embodiment of this very particularly preferred mixture, the mixture comprises at least one compound of the formula (Ia), at least one compound of the formula (Ib), at least 3 compounds of the formula (II) and at least one compound of each of the formulae (VI), (X) and (XI).
In a most preferred embodiment, said at least one compound of the formula (Ia) and at least one compound of the formula (Ib) include at least one compound of the formula (IaIh) and at least one compound of the formula (IaIv) and at least one compound of the formula (IbIa), where in (II) 
is pyrimidine-2,5-diyl, in (VI), Z1 and Z2 are each F, in (X), 
in benzothiazole-2,6-diyl, and in (XI), 
is thiazole-2,5-diyl.
According to one embodiment of the invention, very particular preference is furthermore given to mixtures of the invention which comprise 3 to 30 components, including
4 to 8 compounds of the formula (I)
1 to 10 compounds of the formula (II)
1 to 4 compounds of the formula (IV)
1 to 4 compounds of the formula (VI)
1 to 4 compounds of the formula (X)
1 to 4 compounds of the formula (XI).
In a special embodiment of this very particularly preferred mixture, the mixture comprises at least one compound of the formula (Ia), at least one compound of the formula (Ib), at least three compounds of the formula (II) and at least one compound of each of the formulae (IV), (VI), (X) and (XI).
In a most preferred embodiment, said at least one compound of the formula (Ia) and one compound of the formula (Ib) include at least 1 compound of the formula (IaIh) and at least 1 compound of the formula (IaIv) and, if desired, at least one compound of the formula (IaIn) and at least 1 compound of the formula (IbIa), where, in (II), 
is pyrimidine-2,5-diyl, in (IV) 
is pyrimidine-2,5-diyl, pyridine-2,5-diyl or 2-fluoropyridine-3,6-diyl, in (VI), Z1 and Z2 are each F, in (X), 
is benzothiazole-2,6-diyl, and, in (XI), 
is thiazole-2,5-diyl.
In a particular embodiment of the very particularly preferred liquid-crystal mixture, in
(II) 
xe2x80x83is pyrimidine-2,5-diyl,
Z1, Z2 are both H or both F,
R10 is a straight-chain or branched alkyl or alkyloxy radical having 6 to 14 carbon atoms, where one or two xe2x80x94CH2-groups may be replaced by xe2x80x94Oxe2x80x94 and/or xe2x80x94C(xe2x95x90O)xe2x80x94,
R11 is a straight-chain or branched alkyl or alkyloxy radical having 6 to 14 carbon atoms, where one or two xe2x80x94CH2-groups may be replaced by xe2x80x94Oxe2x80x94 and/or xe2x80x94C(xe2x95x90O)xe2x80x94,
(III) 
xe2x80x83is 2-fluoro-pyridine-3,6-diyl 
xe2x80x83is cyclohexane-1,4-dily
R10 is a straight-chain or branched alkyl or alkyloxy radical having 6 to 14 carbon atoms, where one or two xe2x80x94CH2-groups may be replaced by xe2x80x94Oxe2x80x94 and/or xe2x80x94C(xe2x95x90O)xe2x80x94 and one H atom may be replaced by F
R12 is hydrogen or a straight-chain or branched alkyl or alkyloxy radical having 6 to 14 carbon atoms, where one or two xe2x80x94CH2xe2x80x94 groups may be replaced by xe2x80x94Oxe2x80x94 and/or xe2x80x94C(xe2x95x90O)xe2x80x94.
In a very particular embodiment of the very particularly preferred liquid-crystal mixture,
(II) is 5-alkyl-2-(4-alkyloxyphenyl)pyrimidine, 5-alkyl-2-(4-alkylcarbonyloxyphenyl)pyrimidine, 5-alkylcarbonyloxy-2-(4-alkyloxyphenyl)pyrimidine or 5-alkyl-2-(4-alkyloxy-2,3-difluorophenyl)pyrimidine
xe2x80x83and,
(III) R10 is a straight-chain alkyloxy radical having 6 to 14 carbon atoms, where one H atom is replaced by F
R12 is hydrogen.
The chiralsmectic liquid-crystalline mixture preferably comprises 10-60% of one or more compounds of the formula (I). The mixture particularly preferably comprises 10-60% of 1-15 compounds of the formula (I). The mixture particularly preferably comprises 10-60% of 1-15 compounds of the formula (I) and 40-90% of 2-15 compounds of the formula (II). In particular, the mixture comprises 10-60% of 1-15 compounds of the formula (I), 40-90% of 2-15 compounds of the formula (II) and 1-40% of 1-15 compounds from the group (III), (IV), (V), (VI) and (VII), the total amount being 100%. The percentages are by weight.
The invention furthermore provides compounds of the general formula (I), selected from the compounds of the formula (XX), where
Compounds of the formula (XXI), where: 
is 2-fluoropyridine-3,6-diyl, 4-fluoropyrimidine-2,5-diyl or phenylene-1,4-diyl or possibly pyridine-2,5-diyl, unsubstituted, monosubstituted or disubstituted by F 
is 2-fluoropyridine-3,6-diyl, 4-fluoropyrimidine-2,5-diyl or phenylene-1,4-diyl or possibly pyridine-2,5-diyl, unsubstituted, monosubstituted or disubstituted by F
with the provisos that a) one of the rings W1/W2 must be one of the nitrogen-containing heterocycles and n and m are preferably from 1 to 14 and X is xe2x80x94Oxe2x80x94 or a single bond. n can alternatively be an integer from 2 to 10 and m can be an integer from 3 to 10
or preferably
b) the grasping W1xe2x80x94W2 is undirected and is 3-fluorobiphenyl-4,4xe2x80x2-diyl or 2-fluorobiphenyl-4,4xe2x80x2-diyl, where n, m and X are as defined below
c) the grasping W1xe2x80x94W2 is undirected and is 2,3-difluorobiphenyl-4,4xe2x80x2-diyl, where n and m are from 1 to 14 and X is xe2x80x94Oxe2x80x94 or a single bond.
Further possible combinations are n=9, m=3-10, X=xe2x80x94 and n=8, m=3-10, X=0.
Compounds of the formula (XXII), where:
Compounds of the formula (XXIII), where:
Compounds of the formula (XXIV), where:
Compounds of the formula (XXV), where:
Compounds of the formula (XXVI), where:
Compounds of the formula (XXVII), where:
Compounds of the formula (XXIX), where
Compounds of the formula (XXX), where:
The invention furthermore provides compounds of the general formula (II), selected from compounds of the formula (XXXI), where:
Compounds of the formula (XXVIII), where:
Compounds of the general formula (XXXII), where:
and where Z is H or F in all cases.
Thiophenecarboxylic esters in which the heterocycle may not be fluorinated are generally described in EP-A-0 364 923. EP-A-0 459 406 describes thiophenecarboxylic esters in which the phenyl group has to be substituted by fluorine. In EP-A-0 392 510, the phenylene group has to be 2,3-cyano-substituted.
Tetrahydroquinazolines are generally described in U.S. Pat. No. 4,402,849. An example of compounds of this type can be found in JP-A-08059629, and in JP-A-08062559 and JP-A-07207267.
The examples which follow illustrate the invention. Mixtures according to the invention are given in Examples 1-15.